Avian Interleukin-2 (IL-2) was first identified by Schauenstein et al., Dev. and Comp. Immunol. 6, 533 (1982), who showed the presence of a T-cell growth factor in the supernatant of mitogen-stimulated chicken spleen cells. See also Schat et al., Avian Pathology 15, 539 (1986); Schauenstein et al., in Lymphoid Cell Functions in Aging, 141-147 (A. deWeck ed. 1984); Fox et al., Abstract of Paper Presented at 15th Southeastern Immunology Conference, Stone Mountain Inn, GA, Oct. 20-22, 1982.
Avian IL-2 has subsequently been isolated, to varying degrees of purity, by Schnetzler et al., Eur. J. Immunol. 13, 560 (1983), Vainio et al., Scand. J. Immunol. 23, 135 (1986), and Fredericksen and Sharma, in Avian Immunology. 145-156 (W. Weber and D. Ewert eds. 1987); See also European Patent Application No. 88304729.2. This work, primarily with chicken IL-2, has demonstrated that the lymphokine exists in two configurations: a 13,000 to 14,000 Kilodalton species (hereinafter referred to as "14K chicken IL-2") and a 26,000 to 30,000 Kilodalton species (hereinafter referred to as "30K chicken IL-2").
While considerable work has been done in characterizing the T-cell growth activity of chicken IL-2 in cell culture studies, and work in non-avian species suggests that avian IL-2 may have interesting biological properties when administered to animals, See. e.g., Gillis, J. Clin. Immunol. 3. 1-13 (1983), there has been little mention of a practical use for avian IL-2 in vivo. It would, however, be extremely useful to know if any useful biological effect could be achieved by administering IL-2 to birds.
The present invention arose from our investigations into the biological activity of avian IL-2 in vivo. A particularly important finding disclosed herein is that, when avian IL-2 is administered to birds in ovo, the growth of the treated bird after hatch, as measured by weight gain, is enhanced.